Deflecting device



Dec'. 2, 1941. J. GUNTHER DEFLECTING DEVICE Filed Nov. 22, 1939 FIG. 3.

INVENTOR Patented Dec. 2, 1941 U Nil TAT E. S PAT E N'T FF! C E DEFLECTING DEVICE Johannes I Giinther, Berlin-Zehlendorf; Germany, as signortdFernseh Aktiengesellschaft, Berlin- Zchlendorf, Germany ApplicationNovember 22, 1939, Serial No. 305,697 In Germany N0vembcr'30, 1938 1 Claim.

This invention relates to magnetic deflecting devices for cathode ray tubes particularly for television purposes and it is especially concerned with suitable arrangements and constructions of the coils situated upon an iron yoke.

It is an object of the present invention to provide a deflecting system producing a rectangular scanning field on the screen of the cathode ray tube. It is a further object to avoid so-called pin-cushion distortions of the Scanning field which may be due for instance to the curvature of the screen in case the radius of curvature is larger than the distance between the screen and the deflecting system. These distortions may occur in one or both directions of deflection. It is a further object to reduce or to compensate completely distortions occurring on that side of the scanning field directed towards the deflecting coil situated on the connecting portion of the iron yoke. A further object is to provide a deflecting system which can be used in connection with a cathode ray tube of short length having a wide angle of deflection of the cathode ray in the order of 25 to 35 between the undeflected ray and the maximally deflected ray.

According to the invention the stray field of a coil situated upon the yoke is made use of to compensate the geometrical distortions. Specifically one or more energizing coils are arranged in such proximity to the space through which the cathode ray passes that the stray field of the coils assists in deflecting the cathode ray. In case of a U-shaped yoke it can be preferable to use extensions on the arms of the yoke to produce a compensating field on the side opposite the coil. If I such extensions would be arranged on the side towards the coil they would short circuit a considerable part of the magnetic field. It is therefore a particular advantage to produce the compensation by the stray field of the energizing coil itself. In case a closed yoke is used the coils on both sides of the yoke are arranged so closely to the cathode ray tube that the deflected ray passes on both sides through the stray field of these coils. It is preferable to wind the coils in such a manner that the windings are unevenly distributed over the length of the coil and a desired distribution of the lines of force is produced.

The arrangement has the advantage not only that a linear deflection is made possible over the entire scanned area but also that the deflecting device is made smaller and more compact because the arms of the yoke become considerably shorter. The elflciency of the whole device is increased because the part of the field which does not partake in the deflecting efiect is made very small.

Further objects, features and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawing showing embodiments of the invention in which Figs. 1 and 2 show deflecting yokes with a single deflecting coil,

Fig. 3 a closed deflecting yoke with two coils while Fig. 4 shows a perspective view of a deflecting yoke having pole pieces.

Fig. 1 shows the cross section of a cathode ray tube lying between the arms 2 of a ferromagnetic yoke energized by coil 3. The arms 2 of the yoke may be provided with pole pieces 4, but these pole pieces are not always essential. The ends of the arms carry extensions 5 consisting of soft iron pieces which may be bent in any desired form. The arms of the yoke are made so short that the stray field of coil 3 indicated by dotted lines extends within the tube so that the cathode ray passes through this stray field when it is maximally deflected. It is preferable to arrange the coil in such a manner that the stray lines of force extend into the deflecting space particularly at that point where the greatest distortion would be produced if the stray field were not present. This effect can be increased by giving to the coils a particular cross section as for instance represented in Fig. 2 by coil 6. This coil has a larger diameter in its central portion than at the sides thereof so that the stray field is concentrated in the central part where the maximal distortion occurs. The coil 6 may however be so formed that the cross section in the central portion is smaller than at the edges if for instance a barrel shaped distortion shall be compensated. The stray field may be suitably formed so that it has only an eflect at such places of the deflecting space where its influence is desired. The effect of the stray field is further increased by the fact that the stray field does not only exist in a plane at right angles to the cathode ray but also in planes including a smaller angle with the cathode ray.

Another embodiment of the invention is shown in Fig. 3. The tube l is situated between pole shoes 8 forming a part of arms 1 of a closed yoke. This yoke carries the energizing coils 6 while coils 9 are arranged on the poles for deflecting the cathode ray in a direction vertically to that produced by the coils 6. The stray field of coils 6 enters the cathode ray tube from both sides so that distortions on both sides of the scanned area are compensated.

Fig. 4 shows a view of a deflecting system similar to that of Fig. 2. The extensions 5 may be arranged in the plane of the yoke or as represented in Fig. 4 behind the yoke in the direction of thecathode ray. The effect of these extensions 5 is similar to that of the additional coil 6 of Fig. 3. The arrangement has the advantage that besides a correction of the shape of the scanned area an increase in deflection is obtained. The extensions 5 are preferably so arranged that the end pieces lying opposite to one another are essentially normal to the plane of the screen and parallel to the upper limit of the scanned area. V

The deflecting device of the invention is pare ticularly suited for television transmission and receiving tubes. It is however not limited to the use in these particular types of tubes and can be used in all places where a cathode ray shall be defiected in two directions so that a particular geometric form of scanning patterns is produced.

What I claim is:

A cathode ray deflecting device including an iron yoke having a central portion and two arms between which the main deflecting field exists, a cathode ray tube between said two arms, and an energizing coil, carried by said yoke, said coil having a central portion and two side portions of smaller diameter than the central portion and being so arranged that the cathode ray in its defiected position passes through the stray field of the central portion of said coil.

J OHANNES GUNTHER. 

